1. Field of the Invention
The present invention relates generally to a hydraulic power transmission joint for use in distribution of vehicle driving powers, and more particularly to a hydraulic power transmission joint aiming to prevent a lowering of torque arising from oil leakage and thus from hydraulic pressure reduction.
2. Description of the Related Arts
Conventional hydraulic power transmission joints are known from e.g., U.S. Pat. Nos. 5,706,658 and 5,983,635.
FIG. 1 illustrates an example of a hydraulic power transmission joint being currently developed by the inventors of the present application on the basis of the above Patents, and FIG. 2 is an enlarged view of the major part thereof. Referring to FIGS. 1 and 2, a propeller shaft 101 acting as an input shaft is coupled to a companion flange 102 into which is fixedly inserted a housing shank 104 having a cam face 103 formed on its inner face. A housing 105 is secured by welding to the housing shank 104. The housing shank 104 is supported via a front bearing 106 by a differential gear case 107. A main shaft 108 acting as an output shaft connects with a drive pinion gear 109 associated with a rear differential gear. A rotor 110 is fitted via splines to the main shaft 108 and is rotatably housed in the housing 105. The main shaft 108 is supported via a rear bearing 111 by the differential gear case 107. The rotor 110 is provided with a plurality of axially extending plunger chambers 112 which accommodate plungers 113 reciprocatively under a pressing force of return springs 114, with the plungers 113 being operated by the cam face 103 upon the relative rotations between the two shafts. The plunger 113 has a one-way valve 115 for intake disposed at its head. The rotor 110 is formed with a discharge hole 116 leading to the plunger chambers 112. The discharge hole 116 is provided with a one-way valve 117 for discharge. A valve block 118 coupled to the rotor 110 has a high-pressure chamber 119 leading to the discharge hole 116 and has an orifice 120 acting as flow resistance generating means for generating a flow resistance by the flow of oil discharged by the operation of the plungers. A bearing retainer 121 is securely press-fitted to the housing 105 and is positioned by a snap ring 122. Needle bearings 123 and 124 are interposed between the bearing retainer 121 and the valve block 118 and between the bearing retainer 121 and the main shaft 108, respectively. A thrust washer 125 is further provided between the bearing retainer 121 and the main shaft 108. An accumulator piston 126 is provided for absorbing thermal expansion and contraction of oil residing within the joint.
In such a hydraulic power transmission joint, however, the bearing retainer 121 is supported via the needle bearing 124 by the main shaft 108, whereas the bearing retainer 121 presses the main shaft 108 by way of the thrust washer 125, with the result that rotational secondary torque and thrust-up load input from the propeller shaft 101 enters the interior of the joint and the rotational secondary torque becomes a moment separating the valve block 118 from the rotor 110, allowing a leakage of oil through the gap therebetween, which disadvantageously results in a lowering of toque. The thrust-up load is received by the main shaft 108 while the rotational difference between the input and output is absorbed by way of the thrust waster 125, with the result that abrasions and noises may take place.
More specifically, in FIGS. 1 and 2, the rotational secondary torque is input from the propeller shaft 101 as indicated by an arrow A, passes through the companion flange 102, the front bearing 106, the housing shank 104 and the housing 105 and enters the bearing retainer 121 as indicated by arrows B, C, D, E and F, after which it passes through the needle bearing 124 and acts on the main shaft 108. Via the same route, the thrust-up load enters the bearing retainer 121 and presses the thrust waster 125 to act on the main shaft 108.
Description will then be made of a mechanism of leakage of oil through the gap between the rotor 110 and the valve block 118 as a result of input of such a rotational secondary torque. Referring to FIG. 3, a hydraulic power transmission torque 127 is coupled to a differential gear 128. Rear wheels 129 and 130 are disposed on opposed sides of the differential gear 128. An arrow T indicates an engine torque of the propeller shaft 101. The engine torque T results in a rotational secondary torque as indicated by an arrow Tsin .theta. input to the hydraulic power transmission joint 127. When the rotational secondary torque enters the hydraulic power transmission joint 127, the main shaft 108 of the joint 127 is subjected as in FIG. 4 to a bending force due to a reaction force from the differential gear 128 in the tire lock status as indicated by arrows H of the rear wheels 129 and 130. For this reason, the hydraulic power transmission joint 127 attempts to tilt as indicated by a chain double-dashed line. In effect, however, the hydraulic power transmission joint 127 results by no means in the status of the chain double-dashed line, but instead as in the diagrammatic view of FIG. 5 the housing 105 and the housing shank 104 tend to have a counterclockwise tilt due to a degree of freedom of vertical movement of the propeller shaft 101 in the attached condition. As a result, the rotor 110 becomes tilted relative to the main shaft 108 as shown in FIGS. 6 and 7. In the normal status where input of the rotational secondary torque is absent, the rotor 110 is not tilted relative to the main shaft 108 as in FIG. 8 but remains parallel. Once the rotational secondary torque is input, however, the rotor 110 becomes tilted relative to the main shaft 108 as in FIGS. 6 and 7, resulting in a separation between the rotor 110 and the valve block 118. For this reason, oil may often leak through the gap between the valve block 118 and the rotor 110 and the hydraulic pressure may be reduced with lowering of the torque.